<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>学习jquery对象属性等</title>
</head>
<body>
    <ul>
        <li id="elem"第一个节点></li>
        <li>第二的节点</li>
        <li>第三个节点</li>
        <li>第四个节点</li>
    </ul>
</body>
<script src="./jquery.js"></script>
<script>

    console.log( $("elem") );
    console.log( $("elem").length );

    console.log( $("ul li") );
    console.log( $("ul li").length );

    console.log( $("elem2") )
    console.log( $("elem2").length );
    
</script>
</html>